The first public survey of past Iowa Democratic caucus participants shows 65 percent undecided about which candidate to support. WMJX radio in Boston polled a random sample of 1984 caucus attendees after former senator Gary Hart withdrew from the race last month.

Among the candidates, Rep. Richard A. Gephardt (Mo.) leads with 11 percent; former Arizona governor Bruce Babbitt, who has been targeting caucus-goers with television ads, is next with 6 percent. Jesse L. Jackson and Sen. Paul Simon (Ill.) each have 4 percent. Massachusetts Gov. Michael S. Dukakis 3 percent and Sen. Joseph R. Biden Jr. (Del.) had one percent. Sen. Albert Gore Jr. (Tenn.) is an asterisk, and 5 percent support others.

Phil Roeder, Iowa Democratic Party spokesman, said, "My gut tells me this is the best poll done for the caucuses so far." The results contrast with a recent Des Moines Register poll, which surveys all Iowa Democrats. In that poll, 37 percent were undecided and Gephardt led with 24 percent. Roeder said that only about 20 percent of Democrats turn out for the caucuses. "To poll the majority to figure out what the minority is thinking is wrong," he said.

Of the 1984 attendees surveyed, 61 percent said they definitely intend to go to the 1988 caucuses, 30 percent said they probably will and the rest said they might.